Preparation of Isocyanides

Three routes give isocyanides. (1) FROM PRIMARY AMINES (the carbylamine reaction): both aromatic and aliphatic primary amines, treated with CHCl3 in the presence of KOH, give the corresponding carbylamine -- methylamine gives methyl isocyanide + 3KCl + 3H2O, and aniline gives phenyl isocyanide + 3KCl + 3H2O; this is the same carbylamine test already introduced as a primary-amine identification reaction. (2) FROM ALKYL HALIDES: ethyl bromide heated with ethanolic AgCN gives ethyl isocyanide as the MAJOR product (with ethyl cyanide as a minor by-product) + AgBr -- the ambident cyanide ion attacks predominantly through nitrogen when the metal is silver (contrast with the alkali-cyanide route to alkyl CYANIDES, Section 13.4.2, where attack is predominantly t …